Add section header parsing and use it in the mk-payload step

This completes the improvements to the ELF file parsing code.  We can
now parse section headers too, across all 4 combinations of word size
and endianness. I had hoped to completely remove the use of htonl
until I found it in cbfs_image.c. That's a battle for another day.

There's now a handy macro to create magic numbers in host byte order.
I'm using it for all the PAYLOAD_SEGMENT_* constants and maybe
we can use it for the others too, but this is sensitive code and
I'd rather change one thing at a time.

To maximize the ease of use for users, elf parsing is accomplished with
just one function:

int
elf_headers(const struct buffer *pinput,
	    Elf64_Ehdr *ehdr,
	    Elf64_Phdr **pphdr,
	    Elf64_Shdr **pshdr)

which requires the ehdr and pphdr pointers to be non-NULL, but allows
the pshdr to be NULL. If pshdr is NULL, the code will not try to read
in section headers.

To satisfy our powerful scripts, I had to remove the ^M from an unrelated
microcode file.

BUG=None
TEST=Build a peppy image (known to boot) with old and new versions and verify they are bit-for-bit the same. This was also fully tested across all chromebooks for building and booting and running chromeos.
BRANCH=None

Change-Id: I54dad887d922428b6175fdb6a9cdfadd8a6bb889
Signed-off-by: Ronald G. Minnich <rminnich@google.com>
Reviewed-on: https://chromium-review.googlesource.com/181272
Reviewed-by: Ronald Minnich <rminnich@chromium.org>
Commit-Queue: Ronald Minnich <rminnich@chromium.org>
Tested-by: Ronald Minnich <rminnich@chromium.org>
Signed-off-by: Ronald G. Minnich <rminnich@google.com>
Reviewed-on: http://review.coreboot.org/5098
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
12 files changed